Hosts adjust their defences with information, which in turn influences selection on cuckoos

We know that there is variation across time and space in the ways that hosts defend themselves from parasitism. We also now know that this is usually because of behavioural plasticity, rather than rapid genetic changes among populations. There are costs to removing cuckoo eggs, or mobbing adult cuckoos; so how do hosts best match their defences to risk?

Our work with reed warblers and cuckoos in the UK shows that hosts use both personal and social information to fine-tune their behaviour (see here and here), and the way they use social information has consequences for cuckoos. As reed warblers pay attention to the specifics of the information provided when neighbours mob cuckoos, rare colour forms have an advantage (see here). Current work is investigating how populations of colour morphs vary across host ranges, and how we can use this to test classic theory about Batesian mimics (many cuckoo species mimic dangerous hawks, see here) and polymorphisms.

How hosts acquire information about parasitism may also drive speciation among cuckoos - we are looking at this in the Shining bronze cuckoo that breeds across Australasia - as well as selecting for phenotypic changes in hosts.

Large-scale temporal and spatial variation in host defences is explained by hosts' responses to small-scale variation in parasitism risk, not genetic change. Image by Rose Thorogood.

As hosts use social information to assess parasitism risk, cuckoos are under selection to avoid alerting neighbours. Different colour forms is an effective trick. Click for image details